Treatment of brass



Patented Apr. 20, 1954 TREATMENT OF BRASS Hardy E. Gregory, Kenosha,Wis., assignor to The American Brass Company, Waterbury, Conn, acorporation of Connecticut No Drawing. Application August 24, 1951,

Serial No. 243,587

9 Claims.

IThis invention relates to the treatment of brass and to the fabricationof articles from the treated brass by deep drawing, cold heading, orequivalent operation involving substantial plastic deformation of brasssheet, wire, or other primary shape. The method of the invention entailsa particular preparatory treatment of the primary brass shape, involvingsubjecting it to suffioient cold working to effect a large reduction inarea followed by a recrystallization annealing operation at an unusuallylow temperature. The annealed primary brass shape resulting from thispreparatory treatment has the tensile strength and hardness ofquarterhard or even half-hard cold finished brass, yet it has been foundto be remarkably amenable to fabrication into cups, shells, screws,rivets, and like articles, by operations such as deep drawing and coldheading which involve substantial plastic deformation of the primarymetal shape from which they are made.

In the fabrication of brass articles by deep drawing, cold heading, andlike operations involving substantial plastic deformation, it has beencustomary heretofore to use a primary brass shape which has been fullyannealed and is either in the dead soft condition, or nearly so. Forexample, cartridge brass sheet for deep drawing is usually supplied assoft, fully annealed metal having a tensile strength considerably lessthan 55,000 pounds per square inch, a grain size of 0.025 to 0.050 mm.(or even larger), and a Rockwell "13 hardness of less than 40. Suchmaterial in the cold-finished quarter-hard or half-hard conditionhaving, say,

a tensile I strength of 58,000 pounds per square inch or more and aRockwell B hardness of 00 or more, is unsatisfactory for fabrication bydeep drawing or cold heading methods because it is incapable ofundergoing substantial plastic deformation without the danger ofcracking.

When brass, say cartridge brass or yellow brass, is subjected to suchsevere cold working as to result in a reduction in cross-sectional areaof say 70% or more and is then annealed at the unusually low temperatureof about 375 1 discovered, however, that brass prepared in this fashionis remarkably amenable to fabricating operations entailing verysubstantial plastic deformation, such for example as deep drawingoperations, cold heading operations, etc. I have discovered, forexample, that some forms of deep drawn cups of such design that theycannot be made in a single cut-and-draw operation from ordinarycommercial deep drawing brass strip can, surprisingly enough, be madesuccessfully with a single cut-and-draw from brass sheet prepared asjust described.

Based on these discoveries, the present invention provides a methodwhich comprises subjecting brass containing 5% to 40% by weight of zincand the balance essentially all copper to cold working and thenannealing the brass at a temperature in the range from 500 C. to 600 C.for a sufiicient period of time to effect substantially completerecrystallization without increasing the average grain size to aboveabout 0.045 mm., then subjecting the brass to a severe cold workingoperation sufficient to effect a reduction in cross-sectional areagreater than then annealing the thus worked brass at a term perature ofabout 375 C. for a sufhcient period of time to effect substantiallycomplete recrystallization of the metal without increasing the averagegrain size to above 0.008 mm, whereby the tensile strength of theannealed brass is maintained at a value above 55,000 pounds per squareinch, and then subjecting the thus-annealed brass substantially at roomtemperature to an operation involving substantial plastic deformation.(Throughout this specification and in the appended claims I have forconvenience referred to the tensile strength of the annealed brassfabricated in accordance with the invention as being above 55,000 poundsper square inch. This numerical value is substan tially the averagetensile strength for quartcrhard brass strip composed of or less ofcopper, balance zinc, according to A. S. T. M. specification B36-49-T,or for eighth-hard brass wire of the same composition according to A. S.T. M. specification 13434-49. Itis my intention that this numericalvalue, as used herein, be regarded as substantially such average value,and that in the case of alloys of less than 30% zinc content it beregarded with sufficient flexibility to mean the average tensilestrength, according to said A. S. T. M. specifications, of quarter-hardstrip or eighth-hard wire of such lesser zinc content.) I The brassalloys that may be fabricated with advantage by the method of thepresent invention are alloys containing from 5% to 40% by weight ofzinc, and the balance essentially all copper. I do not exclude, however,the possibility that such brass alloys may include minor amounts ofadditional metals, either by Way of impurities or as metalsintentionally added to impart modified properties to the alloy. Forexample, the alloy may contain, in addition to copper and zinc, a smallamount of lead, or tin, or manganese, or other metal commonly used tomodify the properties of binary copper-zinc alloys or commonly presentas an impurity in such alloys. It is to be understood that thecomposition of the alloy does not in itself form a part of the presentinvention; the invention rather lies in the method of treatingweli-known brasses and then subsequently fabricating the treated brassby a method involving plastic: deformation.

Preparatory to carrying out the method of this invention, the brass issubjected to conventional rolling, drawing, or other primaryworkingoperations until it is brought to its ready-to-finish size andshape. The conventional working methods usedv for this purpose need notbe described in detail. Generally they comprise melting the brass alloy,casting it into a wirebar, cake, or other suitable shape, and thenreducing its crosssectional area by rolling, wire drawing, or otherconventional primary working operation. As the cross-sectional area ofthe metal is reduced by cold working, it becomes hardened and itscapacity to be worked further is lessened. Accordingly, it is customaryto anneal the metal from time to time during the course of the workingoperations, to restore it toa soft condition in which it can readily befurther worked.

After the metal has been brought to its readyto-finish size, it is givena somewhat lighter anneal than is customary by heating at a temperaturein the range from 500 C. to 606 C. for a sufficient period of time toeffect substantially complete recrystallization of the alloy withoutincreasing the grain size above 0.045 (A full recrystallizing anneal ofcold Worked brass at the ready-to-finishsize commonly is at atemperature and for a time sufficient to efieot grain growth to anaverage size of 0.070 to 0.090 mm.)

The term average grain size is used herein, in the manner customary inthe art, to meanthat the average diameter or equivalent dimension of atypical grain is of the size stated. The grains are of course veryirregular in size and shape, but for the most part they are similar toone another in size and shape, and it is customary in referring toaverage grain size to have reference to the most typical size that isfound upon micro scopic examination of the metal structure. In general,the estimation of grain sizes is herein contemplated to be in accordancewith the methods set forth in A.. S. T. M. specification E78- l9-T,entitled. Tentative Methods for Estimating the Average Grain Size of\Vrought Copper and Copper Base Alloys. V

'The annealed metal at ready-to-finish size, with its average grain sizeless than 0.845 mm, is then subjected to severe" cold working (that is,to Working at a temperature below the recrystallization temperature andgenerally at or near room temperature) sufficient to reduce itscross-sectional area by at least 65% and preferably by 70% or more. Themanner in which such cold working is efiected is not in itself critical.It may be by rolling or by drawing through dies,

or by any other cold working method; and it may 7 rolling, drawing, orlike operations is most con venient. However it is done, its efiect mustbe to reduce the cross-sectional area of the worked metal, without anyintermediate anneals, by the amount stated.

At the conclusion of this cold working operation, the metal at itsfinished size and shape. Thus, if the metal has been prepared in sheetor strip form by a rolling operation, it will be at its finishedthickness when this cold working operation is completed; and if it hasbeen prepared by drawing through dies, it will be in the form of rod orwireo-f the desired finished diameter (or other dimension if thefinished shape isnon-circular) The cold worked metal, now at finishedgauge, is subjected to a very unusually light anneal by heating it at atemperature of about 375 C. for a sumci'ent length of time to effectsubstantially complete recrystallization of the metal, but to do sowithout increasing the average grain size: to above 0.008 mm., andpreferably to do. so without increasing the average grain size to above0.0% mm. The: time required forsuch annealing at the rather lowtemperature-oft 0.. is the same as is usually employed at asubstantially higher temperature (say 500 to 550 C.) for-fullrecrystallization of brass for deep drawing to an aver.- age grain sizeof about 0.025: to 01040 Upon completion of this annealing operation,.the brass is found to have the tensile strength and hardness that ischaracteristic of cold finished metal rather than of annealed fullyrecrwtaliized metal. Its tensile strength is upwards of. 55,000 poundsper square. inch, and. advantageously (especially for the alloyscontaining near 30% of zinc) about 60,600 pounds per square inch orhigher. Hardness. of the alloy on the Rockwell 30T scale is above 48,and even 58 or higher in the case of metals showing a tensile strengthof 60,000 pounds per square inch or higher. The metal meets all Of therequirements. of A. S. T. M. specifications B36-49-T' forbrass sheet andstrip in the quarter-hard or even half-hard condition and 5434-49 forbrasswire in the eighthhard or ven quarter-hard condition, even thoughit is fully recrystallized and has not been cold finished.

Because of its evident hardness and high tensile strength, the metalprepared as described above would seem to be a most unpromising materialfor making into articles such as cups and rivets by methods involvingsubstantial plastic deformation, e. g. by deep drawing of strip or bycold heading of wire. Nonetheless, I have found that it does in factpossess a most remarkable ability to undergo such plastic deformation,so that parts can be fabricated from it more readily and with feweroperations than with the softer brass heretofore customarily suppliedfor deep drawing and cold heading operations.

The methods involving plastic deformation by which brass strip or brasswire produced asdescribed above may be fabricated into desired articlesare in themselves conventional. Cupping and deep drawing operations areperformed on the metal in the usual. manner, using conventional,punches, dies and other tools. Likewise, cold heading of brass wireprepared as described above, is carried out in theconventional. manner,using. conventional heading tools- The forces applied to the strip orwire in. such drawing. or heading operations may have to be. a littlegreater than is necessary when working with the heretofore conventionalsoft annealed deep drawing or cold heading brass, but otherwise theoperations are essentially the same.

I have found that brass cups and shells made by deep drawing operationsfrom brass sheet or strip can be formed in many instances more simplywhen using brass prepared as described above than is possible when usingconventional deep drawing brass strip. For example, a deep drawn brasscup having a depth about equal to its diameter and formed with anoutwardly offset and flared lip at its open end has been madesuccessfully in a single cut-and-draw operation from brass stripprepared as herein described. When conventional relatively soft deepdrawing brass was employed in efforts to make this same part in the sameway, the metal invariably tore or cracked in the vicinity of the lip. Inorder to make the part successfully from such soft annealed brass, itwas necessary to subject it to at least two successive drawingoperations. Thus, in making the part according to the invention, thetooling necessary for the deep drawing operation was very muchsimplified and the part was produced more economically and moreefficiently.

Wire prepared as described above may be fabricated successfully in allconventional types of cold heading operations. The wire heads withoutdifficulty on standard cold-heading machines to form virtually everyconventional type of wood or machine screw head, including such complexhead forms requiring severe cold deformation of the metal as washerheads, clutch heads, and fillister heads. For a given tensile strengththe ductility of the Wire, as measured by elongation test, issubstantially twice as great as conventional cold-finished wire, so thatit is unnecessary to make it in special tempers for different types ofheads; and in practice it has been found that the wire is much moreuniform from coil to coil than conventional cold-finished wire.

Another advantage of the method of the invention is that even though themetal is subjected to very severe plastic deformation during the finaloperation of forming the desired article, the finished article itself isvirtually free from any surface roughness of the character known asorange peel. Even in the vicinity of sharp convex curves in deep drawncups, and in cold headed parts where the direction and nature of metalflow has been such as to favor the formation of orange peel, parts madein accordance with the invention are found to have remarkably smoothbright surfaces which require little or no buffing, even when thecharacter of the surface finish is important for decorative purposes.

In consequence of the advantages described above, articles fabricated inaccordance with the invention can in general be made more simply infewer operations and with less complex tooling than has been necessaryheretofore in the fabrication of like articles from conventional softannealed deep drawing or cold heading brass strip, wire or other primaryshape.

Another advantage to the brass mill in preparing metal in the mannerdescribed above is that it can be supplied to the customer in hard coldfinished tempers with substantially fewer cold finishing operations thanare necessary when the metal is prepared by the procedures heretoforeconventionally employed. For example, one common method of'specifyingcommercial degrees of hardness is to call for the brass mill to furnishthe metal rolled or drawn two B&S numbers, or four B818 numbers, or six3&5 numbers, or some number of 3&3 numbers, hard. This terminology meansthat the metal is to have the hardness and tensile strength whichresults from cold finishing fully annealed metal by working it either bycold rolling or by cold drawing by the amount necessary to reduce itsgauge by the specified number of 3&6 gauge numbers. For example, if acustomer asks for brass strip cold finished eight B&S numbers hard, theprocedure heretofore followed for making it is to subject it, after thefinal anneal, to one or more cold rolling operations which reduce itsthickness by eight BdzS gauge numbers. Metal which has been severelycold worked to the extent of more than reduction in area and then giventhe very light anneal at 375 C. as described above is already of thehardness and tensile strength corresponding to what is conventionallyobtained by cold finishing at least two 3&8 gauge numbers hard. If themetal is required cold finished, say, six or eight 3&5 numbers hard,such hardness may be imparted by cold working the annealed metal by anamount corresponding to a reduction of considerably less than thespecified number of B&S gauge numbers, say, by cold working it to theextent necessary to further reduce its crosssectional area by only twoor three 3&8 gauge numbers. In consequence, the manufacture of coldfinished brass in the harder tempers can be achieved more readily byfollowing the practices described above than is possible when using themethods heretofore conventionally employed.

I claim:

1. The method which comprises subjecting brass containing 5% to 40% zincand the balance essentially all copper to cold working and thenannealing it at a temperature in the range from 500 C. to 600 C. for asufficient period of time to effect substantially completerecrystallization without increasing the average grain size to aboveabout 0.045 min... then subjecting the brass to severe cold workingsufficient to effect a reduction in cross-sectional area greater than65%, then annealing the thus-worked brass at a temperature of about 375C. for a sufiicient period of time to effect substantially completerecrystallization without increasing the average grain size to above0.008 mm., whereby the tensile strength of the annealed brass ismaintained at a value above 55,000 pounds per square inch, and thensubjecting the thus-annealed brass substantially at room temperature tosubstantial plastic deformation.

2. The method which comprises subjecting brass containing 5% to 40% zincand the balance essentially all copper to cold working and thenannealing it at a temperature in the range from 500 C. to 600 C. for asufficient period of time to effect substantially completerecrystallization without increasing the average grain size to aboveabout 0.045 mm., then subjecting the brass to severe cold working toeffect a reduction in cross-sectional area greater than then annealingthe thus worked brass at a temperature of about 375 C. for a sufiicientperiod of time r to effect substantially complete recrystallizationwithout increasing the average grain size to above 0.005 mm, whereby thetensile strength of the annealed brass is maintained at a value above60,000 pounds per square inch, and then subjecting the thus annealedbrass substantially at room temperature to substantial plasticdeformation.

3. The method of making a drawn article of sheet brass containing 5%to40% zinc and the balance essentially all copper which comprisessubjecting a bar of such brass to cold rolling and then annealing thebar at a temperature in the range from 500 C. to 600 C. for a sufficientperiod of time to effect substantially complete recrystallizationwithout increasing the average grain size to above about 0.045 mm-.,then cold rolling the bar to a sheet of desired thickness, said coldrolling being sufficiently severe to effect a reduction incross-sectional area of at least 65%, then annealing the sheet at atemperature of about 375 C. for a suiiiicent period of time to effectsubstantially complete recrystallization without increasing the averagegrain size to above 0.008 mm., whereby the tensile strength of theannealed sheet is maintained at a value above 5,000 pounds per squareinch, and then forming the desired drawn. article by subjecting thethus-annealed sheet to a deep drawing operation at room temperature.

4. The method of making a drawn article of brass which comprisessubjecting to a deep drawing operation at room temperature a sheet ofbrass containing to 40% zinc and the balance essentially all copper,said brass sheet being the product resulting from subjecting a bar ofsaid composition to cold rolling and then annealing the bar at atemperature in the range from 500 C. to 600 C. for a sunicient period oftime to eiiect substantially complete recrystallization withoutincreasing the average grain size to above about 0.045 mm, then rollingthe bar to a sheet of desired final thickness by subjecting it to aseries of rolling operations at room temperature, said rolling at roomtemperature being sufficiently severe to effect a total reduction incross-sectional area of at least 70%, and then annealing the thus-rolledsheet at a temperature of about 375 C. for a sufficient period of timeto effect substantially complete recrystallization without increasingthe average grain size to above 0.005 mm., whereby the tensile strengthof the annealed brass is maintained at a value above 60,000 pounds persquare inch.

5. The method of making a headed article of a brass alloy containing 5%to 40% zinc and the balance essentially all copper which comprises colddrawing a wire of such brass and then annealing it at a temperature inthe range from 500 C. to 600 C. for a sufficient period of time toeffect substantially complete recrystallization without increasing theaverage grain size to above about 0.045 min, then cold drawing the wireto finished size, such cold drawing being sufficiently severe to eiiecta reduction in cross sectional area or" at least 65%, then annealing thethus-drawn wire at a temperature of about 375 C. for a sufilcient periodof time to effect substantially complete recrystallization withoutincreasing the average grain size to above 0.008 11 .111., wherebythe'tensile strength of the annealed brass is maintained at a valueabove 55,000 pounds per square inch, and then forming the desired headedarticle by subjecting the thus-annealed wire to a cold headingoperation.

6. The method of making a headed article of brass which comprisessubjecting to a cold heading operation a. brass wire containing'5% to40% zinc and the balance essentially all copper, said brass wire beingthe product resulting from cold drawing a wire of such brass and thenannealing it at a temperature in the range from 500 C. to

600 C. for a sufficient period of time to eifect substantially completerecrystallization without increasing the average grain size toaboveabout0.045 mm., then drawing the wire to finished size by subjecting it to aseries of drawing operations at room temperature, said drawing at roomtemperature being sufficiently severe to efiect a total reduction incross-sectional area of at least 70%, and then annealing the thus-drawnwire at a temperature of about 375 C. for a sufiicient period of time toeffect substantially complete recrystallization without increasing theaverage grain size to above 0.005 whereby the tensile strength of theannealed brass is maintained at a value above 60,000 pounds per squareinch.

7. A deep drawn article of brass containing 5 to 50% zinc and thebalance essentially all copper, said article being the product resultingfrom subjecting a brass bar of said composition to cold rolling and thenannealing the bar at a temperature in the range from 500 C. to 500 C.for a suificient period of time to effect substantially completerecrystallization without increasing the average grain size to aboveabout 0.045 111111., then cold rolling the bar to a sheet of desiredthickness, said cold rolling being sufficiently severe to effect areduction in cross-sectional area of i at least then annealing the sheetat a temperature of about 375 C. for a sufficient period of time toeffect substantially complete recrystallization without increasing theaverage grain size to above 0.008 mm, whereby the tensile strength ofthe annealed sheet is maintained at a value above 55,000 pounds persquare inch, and then forming the desired drawn article by subjectingthe thus-annealed sheet to a deep drawing opera.- tion at roomtemperature.

8. A headed article of brass containing 5% to 40% zinc and the balanceessentially all copper, said article being the product resulting fromcold drawing a wire of such brass and then annealing it at a temperaturein the range from 500 C. to 600 C.'for a suflicient period of time toeffect substantially complete recrystallization without increasing theaverage grain size to above about 0.045 mm., then cold drawing the wireto finished size, such cold'drawing being suiiiciently severe to effecta reduction in cross-sectional area of at least 65%, then annealing thethus drawn wire at a temperature of about 375 C. for a sufiicient periodof time to effect substantially complete recrystallization withoutincreasing the average grain size to above 0.008 whereby the tensilestrength of the annealed is maintained at a value above 55,000 poundsper square inch, and then forming the desired headed article bysubjecting the thus-annealed wire to a cold heading operation.

9. The method of making a plastically deformed article of brass whichcomprises subjecting to substantial plastic deformation at roomtemperature a brass shape which contains 5% to 40% zinc and the balancesubstantially all copper, said shape being the product resulting fromsub- J'ecting brass of said composition to cold working and thenannealing at a temperature in the range,

from 500 C. to 600 C. fora suflicient period of time to effectsubstantially complete recrystallization without increasing the averagegrain size to above about 0.045 mm., then subjecting the brass to severecold working sufficient to effect a reduction in cross-sectional areagreater than 65%, and then annealing thethus-worked brass at atemperature of about 375 C. for a suiiicient period of time to effectsubstantially complete recrystallization without increasing the averagegrain size to above 0.008 mm, whereby the ten- 10 sile strength of theannealed brass is main- Number Name Date tained at a value above 55,000pounds per square 2,188,771 Welch Jan. 30, 1940 inch. 2,190,536 StaigerFeb. 13, 1940 2,280,103 Swartz et a1 Apr. 21, 1942 References Cited inthe file of this patent 5 UNITED STATES PATENTS OTHER REFERENCES v MetalProgress, August 1943, pages 243-248. number Name Date 2,067,076Craighead Jan. 5, 1937 Transactlonszof the A. I. M. M. vol. 156,2,075,233 Heinzel Mar. 30, 1937 10 19441 pages 2,079,239 Barthel May 4:,1937

1. THE METHOD WHICH COMPRISES SUBJECTING BRASS CONTAINING 5% TO 40% ZINCAND THE BALANCE ESSENTIALLY ALL COPPER TO COLD WORKING AND THENANNEALING IT AT A TEMPERATURE IN THE RANGE FROM 500* C. TO 600* C. FOR ASUFFICIENT PERIOD OF TIME TO EFFECT SUBSTANTIALLY COMPLETERECRYSTALLIZATION WITHOUT INCREASING THE AVERAGE GRAIN SIZE TO ABOVEABOUT 0.045 MM., THEN SUBJECTING THE BRASS TO SEVERE COLD WORKINGSUFFICIENT TO EFFECT A REDUCTION IN CROSS-SECTIONAL AREA GREATER THAN65%, THEN ANNEALING THE THUS-WORKED BRASS AT A TEMPERATURE OF ABOUT 375*C. FOR A SUFFICIENT PERIOD OF TIME TO EFFECT SUBSTANTIALLY COMPLETERECRYSTALLIZATION WITHOUT INCREASING THE AVERAGE GRAIN SIZE TO ABOVE0.008 MM., WHEREBY THE TENSILE STRENGTH OF THE ANNEALED BRASS INMAINTAINED AT A VALUE ABOUT 55,000 POUNDS PER SQUARE INCH, AND THENSUBJECTING THE THUS-ANNEALED BRASS, SUBSTANTIALLY AT ROOM TEMPERATURE TOSUBSTANTIAL PLASTIC DEFORMATION.